Vinyl chloride resins stabilized with 2 - mercaptopyridine - 1 - oxide and derivatives



United States Patent 3,533,993 VINYL CHLORIDE RESINS STABILIZED WITH 2 MERCAPTOPYRIDINE 1 OXIDE AND DERIVATIVES Almon G. Hovey, Northford, and Ehrenfried H. Kober, Hamden, Conn., assignors to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Filed June 18, 1968, Ser. No. 737,818 Int. Cl. C08f 45/60, 45/62 US. Cl. 26045.75 6 Claims ABSTRACT OF THE DISCLOSURE Vinyl chloride resins are protected against thermal degradation by the addition of a stabilizing amount of 2- mercaptopyridine-l-oxide or selected derivatives thereof.

This invention relates to a method for stabilizing vinyl chloride resins and to vinyl chloride compositions containing selected stabilizing compounds. More particularly, this invention relates to the use of Z-mercaptopyridine-loxide and certain derivatives thereof to inhibit thermal degradation of vinyl chloride resins.

Synthetic resins of vinyl chloride will partially decompose and discolor when subjected to heat, for example, during molding and fabricating operations, or upon extended storage at elevated temperatures. While discoloration can be tolerated in deeply pigmented resins, it presents serious problems in the manufacture and handling of transparent, translucent and lightly colored vinyl chlorides. Furthermore, such resins are often subject to undesirable growths due to the action of bacteria.

Various heat stabilizers for vinyl chloride resins have been previously disclosed in the art. Thus, US. Pat.

2,888,435 discloses certain substituted tin mercaptide stabilizers, which are effective for this application. However, while providing the desired thermal stabilization, such compounds do not protect the resin from bacterial growth.

2-mercaptopyridine-l-oxide and a wide variety of derivatives thereof have similarly been reported in the literature; these compounds have been disclosed to be excellent biocides for various applications.

Now it has been found in accordance with this invention that 2-mercaptopyridine-1-oxide and selected derivatives thereof are excellent heat stabilizers for vinyl chloride resins. Furthermore, the use of these selected compounds in critical proportions as more fully defined hereinafter confers an additional benefit of mildewcidal action on the vinyl chloride compositions. This dual function in accordance with this invention provides economic and processing advantages in manufacturing vinyl chloride materials in that the use of two different materials to provide mildewcidal action and thermal stabilization, with the attendant problems of chemical interaction, is avoided.

The vinyl chloride resins that may be advantageously stabilized in accordance with this invention include polyvinyl chloride, and the copolymers of vinyl chloride and other polymerizable mono-olefinic compounds which are compatible with the vinyl chloride in polymeric form, that is, which form copolymers with vinyl chloride. Illustrative mono-olefinic compounds include vinyl acetate, methyl methacrylate, vinylidene chloride, the aliphatic fumarates, for example dimethyl fumarate and diethyl fumarate, the aliphatic maleates, for example dimethyl maleate and diethyl maleate, and the aliphatic acrylates, for example ethyl acrylate. The vinyl halide copolymers that may be stabilized in accordance with this invention are copolymers of from 50 to 98% of vinyl chloride, and from 2 to 50% of another copolymerizable olefinic compound. Polyvinyl chloride is particularly advantageously stabilized according to the practcie of this invention.

As previously mentioned, 2-mercaptopyridine-1-oxide, which is fully described in US. Pat. 2,686,786, is an effective heat stabilizer in accordance with this invention. The derivatives of Z-mercaptopyridine-l-oxide suitable for use herein are sodium and calcium 2-mercaptopyridine-1- oxide, which are also described in US. Pat. 2,686,786; the zinc, cadmium and tin, i.e., stannous and stannic, derivatives of Z-mercaptopyridine-l-oxide, as described in US. Pat. 2,809,971; stannous chloride bis-(Z-pyridyl- 1-oxide)disulfide, disclosed in US. Pat. 3,027,372; selected organo-tin derivatives of 2-mercaptopyridine-loxide; and mixtures of the aforementioned compounds. The organo-tin derivatives of 2-mercaptopyridine-l-oxide have the following general formula:

. J O r I wherein R, R and R" are independently selected alkyl, and preferably lower alkyl, i.e., alkyl having 14 carbon atoms; and aryl having 6-10 carbon atoms, preferably phenyl; n and m independently are 0-1 and r is l-2, with the proviso that n plus m plus r is 3. These compounds are fully described in the copending patent application of Charles W. Kaufman, Ser. No. 598,801 filed Nov. 25, 1966, now abandoned, and the application is herewith incorporated in its entirety. Briefly, these organo-tin materials are prepared by reacting an alkali metal salt or ammonium salt of Z-mercaptopyridine-l-oxide with the appropriate organo-substituted tin salt in a solvent system. While any of the organo-tin derivatives represented by Formula I can be suitably employed herein, preferred embodiments of this invention utilize the di(lower alkyl)-, tri(lower alkyl)- and triphenyl-tin compounds. In summary, the preferred compounds used as stabilizing additives for vinyl chloride resin acording to the invention are 2-mercaptopyridine-l-oxide, sodium-Z-mercaptopyridinel-oxide, calcium-Z-mercaptopyridine-l-oxide, zinc-2-mercaptopyridine-l-oxide, cadmium-Z-mercaptopyridine-1- oxide, tin-Z-mercaptopyridine-l-oxide, stannous chloride bis-(Z-pyridiyl-l-oxide) disulfide, di(lower alkyl)tin-2- mercaptopyridine-l-oxide, tri(lower akyl) tin-Z-mercaptopyridine-l-oxide, triphenyl tin-2-mercaptopyridine-1- oxide, and mixtures thereof.

Generally the heat stabilizers of this invention are added to a plastisol comprising one of the aforementioned vinyl chloride resins and a conventional plasticizer. However, the method of incorporation is not critical, and any conventional procedure can be suitably employed. For example, the stabilizer can be dissolved in a suitable solvent and added to the solid resin prior to fabrication. Alternately, the resin, either in powdered or fabricated form, can be sprayed with a solution or suspension of the heat stabilizer according to known techniques.

The stabilizers of this invention are employed in an amount between about .125 and 1,000 p.p.m., and preferably between about 400 and 600 p.p.m. Higher proportions, for example up to and greater than 2,500 p.p.m., can be employed, but generally no additional benefit is recognized by the use of such proportions. Where the concentration of stabilizer in the claims and specification herein is set forth in p.p.m., such concentration is based on the weight of the vinyl chloride resin.

The efficacy of the selected heat stabilizers of this invention is particularly surprising and unexpected in view of the fact that a variety of other closely related derivatives of Z-mercaptopyridine-l-oxide have been found to be ineffective in this application. Thus, as will be apparent from the examples, the barium, strontium and aluminum derivatives of Z-mercaptopyridine-l-oxide do not produce a stabilizing effect upon vinyl chloride resins.'In view of were cast in aluminum dishes and converted to solid the fact that barium and strontium are in the same group elastomers by heating in an oven for various periods at in the Periodic Table as, for example, calcium, it is particspecified temperatures.

ularly surprising that the latter derivative is effective in After observing the color of the cured elastomers, this application while the former are not. Furthermore, mildewcide evalution was porformed in the following certain derivatives of the analogus 2-hydroxypyridine-1- manner: 1% inch squares of elastomer were cut and oxide have been found to be ineffective as heat stabilizers placed in the center of culture dishes containing 19 cc. for vinyl chloride resins, thereby substantiating the selecof agar and inoculated with a broth containing a fresh tivity of the compounds suitable for use herein. 7 day old culture of Pullularia pullans. In accordance with The stabilized vinyl chloride compositions of this inconventional bacteriological procedures, each dish revention may be used for the production of various fabriceived the same quantity of spores. The specimens were cated structures such as film, sheets, bars, rods, etc., in kept in a high humidity environmental room maintained accordance with known techniques. Furthermore, convenat 75 F., 81% relative humidity and examined at intertional additives such as fillers, light-colored pigments and vals for organism growth. the like may be added to the compositions prior to fabri- The following table shows data for plastisols compriscation into the desired end product. ing 42.8 parts dioctyl phthalate and 58.2 parts polyvinyl The following examples will serve to illustrate the chloride, which were cured for minutes at 180 C. practice of this invention. All parts and percentages are The following tables indicate the performance of these by weight unless otherwise specified. compositions:

TABLE I Hildeweide evaluation Example 2-rnei'captopyridino l-oxide derivative Color lweek 2weeks 3Weeks 4weeks Control." None Dark brown Black and green Black and green Agar completely Starting growth mold on agar mold heavy. overgrown. on plastic. 1 Tin (II) Lighter brown I I I T.

than control. 2 Stannous chloride bis-(Z-pyridyl-ldo I I l I.

oxide)disulfide.

EXAMPLES Data for plastisols based on parts polyvinyl chloride and 50 parts epoxidized soyean oil having an oxirane con- Various plastisols were made by grinding 1000 ppm. tent of approximately 6.04% are set forth herein. The (based on total plastisol weight) of the indicated stabil- 35 plastisols were cured by heating at 175 C.

TABLE II Mildeweide evaluation Example 2-mercaptopyridine-l-oxide derivative Color 1 week 2 weeks 3 weeks 4 weeks Control-.. None Dark orange to Agar completely Creeping up edges Appears to be Starting growth amber. ogergrown over of plastic. startling growth on plastic. 0 es. on asti 3 Sodium Light orange 1--.? I I I. 4 Zine Water White I I I I.

transparent. 5 Triplienyl tin Light yellow to I.Z 3/32 I.Z Invasion of pre- Definite invasion orange. vious I.Z. of previous I.Z. starting. 6 Star nous chloride bis-(2-pyridyl-1- Light orange to 0 I.Z I.Z. on 2 sides Same as at 2 Pullularia all over oxide)disulfide. only. weeks. agar; white over one corner of I sample. 7 Tin (IV) Light orange to 0 I.Z Irreg. I.Z Smaller I.Z. Agar completely covered; none on sample. 8 'Iributyl tin Slight yellowing- I .Z K to I.Z to V I.Z to I.Z. 9 Tin (II) Medium orange- I.Z Very small I.Z Agar covered Agar covered;

edges covered;l H0118 O11 samp e. 10 Dibutyl tin Light yellow I.Z to I.Z I.Z. getting Large I.Z. on

smaller. 2 sides.

izer in a porcelain mortar, adding slowly, with thorough The following table shows data for plastisols having mixing, the appropriate plasticizer, and then blending 1nto the same base ingredients in the same proportions as those the stabilizer-plasticizer dispersion Goodrich Pl-iovic reported in Table II. Curing was effected by heating at WO2, a plastisol grade polyvinyl chloride. The plastisols 180 C. for 40 minutes.

TABLE III Mildeweide Evaluation 2-mereaptopyridme4- Example oxide derivative Color 1 week 2 weeks 3 weeks 4 weeks ControL.- None Deep orange Agar eovered- Creeping up over Appears to be stai't- Definite though slight starting over top edges. ing growth on growth on top of of sample. plastic. sample. 11 Zinc Very light yellow" to I.Z About 30% Agar- Very large I.Z to I.Z.

covered along outer perimeter. 12 Tin (IV) Medium orange.-- Less than I.Z Very small I.Z Very small I.Z Very small I.Z. on

one side 0111 13 Tributyl tin Medium yellow to I.Z to I.Z. all to I.Z. all to W I.Z.iill around sample. around sample around sample.

14 Dibutyl tin .do to I.Z Definite I.Z I.Z M6 to I.Z. on 2 sides.

What is claimed is:

1. A composition comprising:

(a) a vinyl chloride resin and (b) a stabilizing amount of a compound selected from the group consisting of Z-mercaptopyridine-l-oxide, sodium 2 mercaptopyridine 1 oxide, calcium-2- mercaptopyridine-l-oxide, zinc-2-mercaptopyridinel-oxide, cadmium-2-mercaptopyridine-l-oxide, tin-2- Data for plastisols formulated as described in Tables II and HI and cured at 200 C. for 10 minutes is reported herein. Comparative Examples 1-3 indicate the inffectiveness of related Z-mercaptopyridine-l-oxide derivatives 5 in the process of this invention.

TABLE IV Mildewcide evaluation Example Z-mercaptopyridine-l-oxide derivative Color 3 Days Control None Definite yellow orange tint V.E. C-l Aluminum do Very large 1.2 0-2 Barium do Complete inhibition. 0- Strontium do o. 2-mercaptopyri light yellow... V E 16. Zine Water white, tr p V.E. 17 Calcium Almost water white Almost complete inhibition.

20 mercaptopyridine-l-oxide, stannous chloride bis-(2- The following table reports data for plastisols formupyndyl 1- igl g q f i tl 'g' lated as in Tables II-IV and cured at 200 C. for mercaptopyrl '9 1( ower. a y) minutes. Examples employing the barium strontium and mercaptopyndme'l'oxlde mphenyl tm'z'mercapto' pyridine-l-oxide, and mixtures thereof. $25133 i gggg sg 2 mercaptopyndme 1 oxlde an 25 2. The composition of claim 1 in which said stabilizing amount ranges from about 125 to about 2500 parts per one million parts by weight of said vinyl chloride resin.

TABLE V Mildeweide evaluation Example 2-mercaptopyridine1-oxide derivative Color 3 Days Cherry red brown V.E.

Deep orange Large I.Z.; Agar 20% covered. glom lete inhibition.

g Oadmium. Very light yellowery small I.Z.

19 Zine do V.E.

20 Calcium Light yellow GAOA.

' 3. The composition of claim 1 wherein said compound For purposes of further comparison, various salts of 2- 40 is sodium-Z-mercaptopyridine-l-oxide. hydroxypyridine-l-oxide were tested as heat stabilizers for 4. The composition of claim 1 wherein said compound polyvinyl chloride resins, employing the same formulais stannous chloride bis-(2-pyridyl-1-oxide)disulfide. tions as in Tables II-V, and curing at 200 C. for 30 5. The composition of claim 1 wherein said compound minutes. As will be apparent from the following table, is di(lower alkyl) tin-Z-mercaptopyridine-l-oxide. these salts were ineffective in this application. 6. The composition of claim 1 wherein said compound is tri(lower alkyl) tin-Z-mercaptopyridine-l-oxide.

TABLE VI Mildewcide evaluation Example Z-hydroxypyridine-l-oxide derivative Color 3 Days Chen'y red brown Very deep orange Aluminum. Very deep orange to brown V.E.

0-9 Strontmm Deep orange Complete growth on sample.

NOTE.-II1 the above tables: I=Complete inhibition; IzzInhibition zone; VEzGrowth starting up edge of plastic; GA A: Growth all over agar-m0 LZ.

References Cited UNITED STATES PATENTS 2,564,646 8/1951 Leistner et a1. 26045.7 2,632,747 3/1953 Darby 26023 2,809,971 10/1957 Bernstein et al 260270 3,096,183 7/1963 Genth 106l5 3,154,518 10/1964 Gradsten et a1. 260--45.9 3,214,453 10/ 1965 Stern 260429.7 3,288,669 11/1966 Hechenbleikner 167-22 3,308,082 3/1967 Pauli et al. 26029.5 3,321,480 5/1967 Schroder et a1. 260270 DONALD E. CZAJA, Primary Examiner R. A. WHITE, Assistant Examiner US. Cl. X.R. 260--45.8; 424-78 

